Question about thunderbolt docks.

David82 · April 9, 2021

Ok, so if you look back at my post history you will see that I had some fun last year trying to get a couple of dell laptops to both work with a Dell WD19TB dock with dual 4k monitors @60hz.

I managed to get the whole thing working with a mess of cables and an adaptor to allow me to plug two display port cables into the monitor and switch between which one was connected.

I have an update and a question.

So the update is that I changed clients and so the crappy old dell has been replaced with a new Lenovo with a Ryzen CPU... This immediately worried me because I didn't think that my thunderbolt dock would work at all luckily when I got it home I gave it a go and it just works, literally no config nothing plugged it in and it works straight away (The fact that my dell dock works better with a lenovo laptop than a dell laptop is astounding to me).

Fast forward to today... I noticed something strange, I had accidently unplugged the Thunderbolt -> display port adaptor on the dock but both screens were still working both at 4k@60hz and that leads to my question... How is that possible? the documentation for the dock says that to get 4k@60 out of two monitors you have to use one dp connection and the thunderbolt connection no other combination of ports will work.

But I now have my lenovo laptop connected to the dock and two monitors connected to the dock to the DP ports and its working fine... Just tried it again with my XPS 9550 and yep that only works with the DP + TP ports.

So what's so different about the lenovo laptop that I dont have to use the TB port for display output?

Attached a couple of images of the dock showing how its connected - Hope you appreciate the ghetto mount for it, I bought the official dell mounting bracket and then realised that because of the metal frame under my desk that it doesnt actually fit unless I raise it up 3cm so thats a £300 dock attached to a £45 mounting bracket held onto the desk with £0.25 of scrap wood that was lying in the garage

Lenovo Model is Thinkbook 14 G2 ARE, Dell is a xps 9550, dock is a WD19TB

DejaVoodoo · April 9, 2021

Dell docks monitor support relies on the GPU of your laptop..so if your laptop doesn't support it the dock won't.

David82 · April 9, 2021

20 minutes ago, DejaVoodoo said:

Dell docks monitor support relies on the GPU of your laptop..so if your laptop doesn't support it the dock won't.

That makes sense, so the documentation for the dock is wrong, or at least misleading as it's down to the laptop it's connected to rather than the dock itself that determines what ports will/won't work for 4k60

Then again BOTH laptop support 4k@60 to dual monitors*, it's the dock that imposes the limitation on the connections that are used, im still confused.